Group lexical context variables for faster look up.

src/runtime/runtime-scopes.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/arguments.h"
 #include "src/frames-inl.h"
 #include "src/messages.h"
@@ skipping 18 matching lines @@
 }
 
 
 // May throw a RedeclarationError.
 static Object* DeclareGlobals(Isolate* isolate, Handle<GlobalObject> global,
                               Handle<String> name, Handle<Object> value,
                               PropertyAttributes attr, bool is_var,
                               bool is_const, bool is_function) {
   Handle<ScriptContextTable> script_contexts(
       global->native_context()->script_context_table());
-  ScriptContextTable::LookupResult lookup;
-  if (ScriptContextTable::Lookup(script_contexts, name, &lookup) &&
-      IsLexicalVariableMode(lookup.mode)) {
+  // We use LookupLexical to limit lookup to lexical variables. As long as
+  // lexical variables are not used extensively, this is a performance win.
+  // TODO(yangguo): reconsider this shortcut.
+  if (ScriptContextTable::LookupLexical(script_contexts, name)) {
     return ThrowRedeclarationError(isolate, name);
   }
 
   // Do the lookup own properties only, see ES5 erratum.
   LookupIterator it(global, name, LookupIterator::HIDDEN_SKIP_INTERCEPTOR);
   Maybe<PropertyAttributes> maybe = JSReceiver::GetPropertyAttributes(&it);
   if (!maybe.IsJust()) return isolate->heap()->exception();
 
   if (it.IsFound()) {
     PropertyAttributes old_attributes = maybe.FromJust();
@@ skipping 565 matching lines @@
                                                                 pretenure_flag);
 }
 
 static Object* FindNameClash(Handle<ScopeInfo> scope_info,
                              Handle<GlobalObject> global_object,
                              Handle<ScriptContextTable> script_context) {
   Isolate* isolate = scope_info->GetIsolate();
   for (int var = 0; var < scope_info->ContextLocalCount(); var++) {
     Handle<String> name(scope_info->ContextLocalName(var));
     VariableMode mode = scope_info->ContextLocalMode(var);
-    ScriptContextTable::LookupResult lookup;
-    if (ScriptContextTable::Lookup(script_context, name, &lookup)) {
-      if (IsLexicalVariableMode(mode) || IsLexicalVariableMode(lookup.mode)) {
+    if (IsLexicalVariableMode(mode)) {
+      ScriptContextTable::LookupResult lookup;
+      if (ScriptContextTable::Lookup(script_context, name, &lookup)) {
+        return ThrowRedeclarationError(isolate, name);
+      }
+    } else {
+      if (ScriptContextTable::LookupLexical(script_context, name)) {
         return ThrowRedeclarationError(isolate, name);
       }
     }
 
     if (IsLexicalVariableMode(mode)) {
       LookupIterator it(global_object, name,
                         LookupIterator::HIDDEN_SKIP_INTERCEPTOR);
       Maybe<PropertyAttributes> maybe = JSReceiver::GetPropertyAttributes(&it);
       if (!maybe.IsJust()) return isolate->heap()->exception();
       if ((maybe.FromJust() & DONT_DELETE) != 0) {
@@ skipping 521 matching lines @@
 
   // Lookup in the initial Object.prototype object.
   Handle<Object> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result,
       Object::GetProperty(isolate->initial_object_prototype(), key));
   return *result;
 }
 }  // namespace internal
 }  // namespace v8